The present invention relates to a driver device which causes a vibrator to produce driving vibrations, a physical quantity measuring device (e.g. vibrating gyroscope) using the driver device, and an electronic instrument.
Gyroscopes are classified as a rotating gyroscope, a vibrating gyroscope, and the like depending on the method of detecting the force exerted on an object. In particular, the vibrating gyroscope is considered to be advantageous for reducing the size and cost from the viewpoint of the constituent elements and the like. As the vibrating gyrosensor which detects the angular velocity exerted on an object, a piezoelectric vibrating gyrosensor is known which excites a crystal or a piezoelectric element which is advantageous for increasing the reliability and reducing the size. The piezoelectric vibrating gyrosensor utilizes a phenomenon in which, when the angular velocity is applied to a vibrating object, a Coriolis force occurs perpendicularly to the vibrations.
The vibrating gyrosensor is used in a wide variety of applications, such as shake detection for a video camera or a digital camera, positioning using a global positioning system (GPS) for a car navigation system, and position detection for an aircraft or a robot.
The vibrating gyrosensor used in these applications is driven by a battery. Therefore, it is necessary to increase the life of the battery by reducing the power consumption of the vibrating gyrosensor as much as possible. In this case, it is preferable to stop supplying power to the vibrating gyrosensor when the angular velocity or the like is not detected and to supply power to the vibrating gyrosensor from the battery only when using the vibrating gyrosensor. This makes it necessary to cause the vibrating gyrosensor to perform a normal operation within a short period of time after activation.
JP-A-2004-286503 and JP-A-2003-240556 disclose technologies for reducing the startup time of the vibrating gyrosensor, for example. JP-A-2004-286503 discloses technology in which a CR oscillation circuit or a ring oscillator is provided in an oscillation loop so that the oscillation amplitude is increased by an amplifier immediately after activation. JP-A-2003-240556 discloses technology in which a resistor is provided in series with a crystal vibrator to reduce the period of time until the signal from the vibrator is stabilized.
A driver device for the vibrating gyrosensor must cause the vibrator to constantly vibrate (oscillate) at a resonance frequency in order to stably detect the angular velocity exerted on the vibrator. The driver device also must cause the vibrator to oscillate within a short time to start a normal operation. Moreover, it is preferable to form the driver device using a small circuit with low power consumption in order to increase the life of the battery at low cost.
On the other hand, if the vibrator is formed of a crystal having a high Q-value and sealed in a package under vacuum, the Q-value of the vibrator increases to a large extent during drive. Therefore, the period of time (startup time) until the signal from the vibrator is stabilized increases when causing the vibrator to produce driving vibrations.
According to the technology disclosed in JP-A-2004-286503, when causing the crystal oscillator to oscillate at a frequency close to the driving frequency of the crystal oscillator, the areas of the capacitor and the resistor of the CR oscillation circuit must be increased. This results in an increase in the size and cost of the vibrating gyroscope (vibrating gyrosensor). According to the technology disclosed in JP-A-2004-286503, it is difficult to cause the crystal oscillator to operate at the driving frequency of the crystal oscillator with a high Q-value since the crystal oscillator is driven at another frequency during startup. Therefore, the period of time until stable oscillations are achieved increases when affected by a manufacturing variation and the like.
The technology disclosed in JP-A-2004-286503 requires a gain control circuit which controls the oscillation amplitude in the oscillation loop and the like in order to satisfy the oscillation conditions while preventing destruction of the vibrator, whereby the circuit scale and power consumption increase.
According to the technology disclosed in JP-A-2003-240556, it is necessary to insert a resistor. In general, when incorporating a resistor in an integrated circuit device, it is difficult to apply the desired energy to the vibrator due to a large manufacturing variation of the resistor.
According to the technology disclosed in JP-A-2003-240556, the gain is reduced because the energy applied to the vibrator is divided by the resistor. Furthermore, the technology disclosed in JP-A-2003-240556 requires a gain control circuit which controls the oscillation amplitude in the oscillation loop and the like in order to satisfy the oscillation conditions while preventing destruction of the vibrator, whereby the circuit scale and power consumption increase.